1. Field of the Disclosure
The present disclosure relates to alkynyl-substituted glycolides and in particular, the acetylene-functionalized glycolide monomer, 3,6-dipropargyl-1,4-dioxane-2,5-dione (1). The subsequent polymerization of the glycolide 1 provides a poly(glycolide) polymer as a homopolymer of glycolide 1 as well as random and block copolymers with lactide. The poly(glycolide) polymers have pendant alkynyl groups available for the attachment of functional groups (e.g., azide-substituted organic compounds) using “click” chemistry to form a covalent triazole link between the poly(glycolide) polymer backbone and the desired functional group.
2. Brief Description of Related Technology
The biodegradability and biocompatibility of aliphatic polyesters have established polymers derived from lactide, glycolide and ε-caprolactone as key materials for biomedical applications. However, the parent homopolymers have limitations. For example, they are often too hydrophobic for applications in aqueous environments, and more importantly, they lack chemical functionality that enables modification of the polymer backbone. Recent work describes successful strategies for appending hydroxyl1-3, carboxyl4, poly(ethylene oxide) (PEO)1,5-7, allyl8-9, and acetylene5 functionalities to polyesters by co-polymerization with functional monomers, post-polymerization modification of polymers, or a combination of these two approaches.
The functional monomer approach involves multi-step synthetic procedures each time modification is desired. Moreover, the functionality that is introduced must be compatible with polymerization conditions. Similarly, post-polymerization modification requires careful control of reaction conditions to avoid backbone degradation.
Because of its high selectivity, reliability, and tolerance to broad range of functional groups and reaction conditions, “click” chemistry, specifically the copper(I)-mediated 1,3-dipolar cycloaddition of azides and alkynes, is a powerful strategy for elaborating polymer architectures.10-11 “Click” chemistry has been used for the preparation of block copolymers12,13, cross-linked adhesives14, dendrimers15-18, and the introduction of pendant and terminal functional groups into various polymers including polyesters.5,7,19-26 
The Ernrick group first described the use of aqueous “click” chemistry to graft azide-terminated PEO and peptides onto polyesters containing pendant acetylene groups.5 Later, Jerérôme and coworkers found Emrick's conditions caused significant backbone degradation during functionalization.7 Using less severe conditions (THF as the solvent), they were able to introduce PEO, tertiary amines and ammonium salts onto caprolactone-based polyesters having pendant azides. Unfortunately, lactide copolymers are more hydrolytically sensitive than caprolactones, requiring capping of the polymer hydroxyl groups to avoid significant backbone degradation under Jerérôme's conditions. In addition, “click” reactions using CuI, the catalyst used by Jerérôme, are subject to more side reactions than Cu(I) catalysts generated in situ.27 
The properties of polyglycolides have been tailored through the synthesis and polymerization of substituted glycolides. Successfully prepared substituted glycolides include poly(phenyllactide)28, polymandelide29, alkyl-substituted polyglycolides30, allyl-substituted polyglycolide31, PEO-substituted polyglycolides, and alkyl/PEO-substituted amphiphilic polyglycolides.32 Baker et al. U.S. Pat. No. 6,469,133 relates to polymers of cyclic esters, and is incorporated herein by reference in its entirety.